The present invention relates generally to a counterbalance mechanism to counterbalance the weight of an overhead garage door during opening and closing movements and in particular to a counterbalance torsion spring assembly and the method of installation and adjustment of the counterbalance torsion spring to an overhead garage door.
Torsion spring counterbalancing mechanisms have been employed for many years to counterbalance overhead garage doors as they move up to an open position and down to a closed position. Until the present invention, installation of torsion spring counterbalance mechanisms for operation with the garage door required winding the torsion spring until a desired torque is achieved for desired counterbalancing. Frequently, this involves repeated trial and error manual winding and unwinding maneuvers against the high torque of the torsion spring until the proper balance against the weight of the garage door is achieved. Presently, such maneuvers involve the use of one successively or two lever bars that are successively inserted into circumferentially spaced apart sockets or openings in a plug or spider at a free end of the torsion spring. Initially, the installer, using the lever bar rotates the free end of the torsion spring in the direction that winds the torsion spring relative to the fixed end of the torsion spring. As the torsion spring is wound it produces a tremendous unwinding torque. The lever bar must be repeatedly removed from and reinserted into a different socket or opening in the plug or spider at the end member in order for the installer to maintain leverage against the tremendous unwinding torque and prevent a violent unwinding of the torsion spring. It is also necessary to similarly use a second lever bar or other tool to hold the torsion spring in place while the other lever bar is repositioned. A typical installation requires 28 such maneuvers as the torsion spring requires 28 quarter turns to be fully wound. When winding has been completed it is necessary to secure the free end of the torsion spring to the torsion shaft. Typically, two torsion springs are employed and each must be carefully wound and properly adjusted upon installation of the garage door and counterbalance mechanism to the surrounding garage door framework.
Various attempts have been made in the prior art to address this situation and to reduce the possibility of a violent unwinding of the torsion spring as it is wound upon installation. Examples of such attempts are self-locking worm gear mechanisms disclosed in U.S. Pat. No. 3,921,761 to Votroubek et al and U.S. Pat. No. 4,882,806 to Davis. However, such self-locking worm gear mechanisms still require the time and labor involved in performing an initial winding operation during installation. Furthermore, such mechanisms also add to the complexity and cost of a torsion spring counterbalance assembly while detracting from its reliability and do not provide for independent adjustment of the winding drum or reels as provided by the present invention.
It is an object of the present invention to eliminate winding of a counterbalance torsion spring for an overhead garage door during installation to improve the safety while reducing the time and labor of such installation.
It is a further object of this invention to provide a torsion spring counterbalance mechanism in which the torsion spring is prewound and the counterbalance mechanism is pre-assembled prior to installation.
It is a further object of this invention to facilitate adjustment of the tension of the torsion spring at either end of the torsion shaft with the garage door in the open position with minimum unwinding torque from the torsion spring.
It is a further object of this invention to enable the torsion spring counterbalance assembly to be installed and serviced with standard tools, obviating the use of lever bars, by other than experienced professional garage door installers and service personnel.
It is a further object of this invention to independently adjust the length of a winding band wound about separate winding drums disposed on each side of the garage door for proper leveling of the garage door relative to the counterbalance mechanism.
It is a yet further object of this invention to provide a torsion spring counterbalance mechanism for an overhead garage door that not only has the above advantages but also uses a minimum number of parts that are standardized and non-handled to the fullest extent possible with an accompanying reduction in inventory costs at both the factory and distributor.